LONGITUDINAL EVALUATION OF MALARIA EPIDEMIOLOGY IN AN ISOLATED VILLAGE IN WESTERN THAILAND: I. STUDY SITE AND ADULT ANOPHELINE BIONOMICS.

ABSTRACT

This is the first in a series of papers describing the epidemiology of malaria in an isolated village in western Thailand. The study site was the village of Kong Mong Tha, located in Sangkhla Buri District, Kanchanaburi Province, Thailand. In this paper we present an overview of the study site and results from our adult anopheline mosquito surveillance conducted over 56 consecutive months from June 1999 until January 2004. The collection site, indoor/outdoor location, parity, biting activity and Plasmodiumfalciparum (Pf) and P. vivax (Pv) infection rates were used to calculate seasonal entomological inoculation rates for the predominant four Anopheles species. A total of 21,566 anophelines representing 28 distinct species and 2 groups that were not identified to species were collected using human bait, with almost 95% of the collection consisting of Anopheles minimus, An. maculatus, An. sawadwongporni and An. barbirostris/campestris. Mosquitoes generally peaked during the wet season, were collected throughout the night, and were collected most often outside (ca. 75%) versus inside (ca. 25%) of houses. Approximately 50% of collected mosquitoes were parous. Overall Plasmodium infection rates were 0.27%, with a total of 16 and 42 pools of Pf- and Pv-positive mosquitoes, respectively. Annual EIRs were 2.3 times higher for Pv than for Pf, resulting in approximately 5.5 and 2.6 infective bites per person per year, respectively. The results suggest An. minimus and An. maculatus are the primary and secondary vectors of Pf and Pv transmission in Kong Mong Tha, while An. sawadwongporni and An. barbirostris/campestris also appear to play a role based on the presence of circumsporozoite protein (CSP) in the head/thorax of the specimens tested.